Zn/Cu complexes constructed through selective in situ Br–Cl exchange: synthesis, structures, properties, and DFT insights into the Cu-catalyzed mechanism

Abstract

Two coordination polymers (CPs), [Cu₂(L₁)(μ₃-OH)(H₂O)]_n (1) and {[Zn₄(L)₂(4,4′-bipy)₃]·4H₂O}_n (2), were synthesized under solvothermal conditions. Unexpectedly, the transformation of aryl–Br to aryl–Cl (Br–Cl exchange) was observed in the formation of complex 1, which was successfully proven via energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Strikingly, Cu(II) ions were utilized as both coordinated atoms and as a catalyst for the in situ Br–Cl exchange in the process. In contrast, 5-(3-bromo-4-carboxyphenoxy)isophthalic acid (H₃L) did not exhibit any change in complex 2. Moreover, the Br–Cl exchange mechanism on aromatic rings of H₃L was investigated using density functional theory (DFT) calculations. More importantly, selective in situ metal/ligand reactions are important for the discovery of new ligands and synthetic organic chemistry. In addition, complex 1 exhibits a (3,6)-connected topological network, which shows dominant antiferromagnetic exchange in the tetranuclear Cu(II) unit. Complex 2 shows a (3,4,5)-connected topology with strong fluorescence intensity and its fluorescence lifetime (16.0 μs) was obtained using the formula [(A₁ × τ₁²) + (A₂ × τ₂²)]/(A₁ × τ₁ + A₂ × τ₂).